Semiconductor devices have a significant role in solving energy challenges. Specifically, nitride power transistors have great potential in the application of advanced transportation systems, reliable energy delivery networks and many new approaches for high-efficiency electricity generation and conversion. Those systems rely on very efficient converters to step-up or step-down electric voltages. Most of these devices are made of silicon (Si). However, the limited breakdown voltage and frequency response of Si, and its higher resistance make the commercial devices and circuits currently available very bulky, heavy and inappropriate for future power applications. As an alternative, gallium nitride (GaN) devices have achieved record combination of high-voltages, high frequency response and low on-resistances for power applications.
GaN power devices, such as the GaN-based high electron mobility transistors (HEMTs), are regarded as one of the most promising candidates for high-power, high-voltage and high frequency applications. GaN HEMTs have achieved up to 10 times higher power density of GaAs HEMTs with much larger breakdown voltage (VB) and current density, as well as a high cut-off frequency of over 400 GHz. State-of-the-art power levels have been demonstrated on silicon carbon (SiC) substrates with total output powers of 800 W at 2.9 GHz and over 500 W at 3.5 GHz. However, for the high-power applications, such as high-power motors, a higher output power, i.e. 3˜5 kW, is desired, which requires a further enhancement of output power of semiconductor devices.